The present invention relates to screws and to screwdrivers for applying torque to the screws by manual or mechanical force.
A screwdriver for applying torque to a screw typically comprises a shank whose free end or tip is configured in complementary fashion to a socket formed in a head of the screw so as to be capable of mating with, and transmitting torque to, the screw.
Manual screwdrivers which are commercially available include, at their tips, drive surfaces which face in the direction of rotation to engage correspondingly oriented driven surfaces of the screwdriver. For example, a flat-headed screwdriver possesses radially extending drive surfaces which face in the direction of rotation; Torx and Phillips screwdrivers possess longitudinally extending drive surfaces which face in the direction of rotation. The tips of the Torx and Phillips screwdrivers may possess a taper, e.g., from 10.degree. to 50.degree., to facilitate entry of the tip into the screw socket.
Further, there have been proposed so-called tamper-resistant screws which so termed that because they resist being unscrewed by conventionally shaped screwdriver tips. For example, as disclosed in German OS 26 08 892, a screw is provided with a multi-lobed socket each lobe of which is configured as a segment of a cone having a taper (i.e., cone angle of approximately 3.degree.). The screwdriver tip has multiple sides correspondingly curved to mate with the screw socket. In that type of arrangement, there are no torque-transmitting surfaces facing in the direction of rotation. Rather, the torque is transmitted from a radially outwardly facing surface on the screwdriver to a radially inwardly facing surface in the screw socket. However, the curved sides of the screwdriver intersect one another to form generally sharp edges. Since, as noted above, the torque is transmitted between radially facing surfaces, there may occur a tendency for the screwdriver to be cammed out of the socket during a turning operation. As that occurs, the sharp edges will tend to cut the lobes of the screw socket in a manner causing the socket to become rounded and thus unable to be properly driven by the screwdriver.
It would be desirable to provide a screwdriver/screw arrangement of the latter type which is easier to make and use and which minimizes any tendency for the screwdriver tip to cut the sides of the screw socket.
Screwdrivers have also been utilized in automated equipment, as exemplified by Lahm U.S. Pat. No. 4,700,442. In order to regulate the torque applied to the screw, the screwdriver includes two shank sections rotatably interconnected by inclined slide faces. The two shank sections are yieldably urged together by a spring. When the rotary torque exceeds a threshold value, the slide faces move axially relative to one another and terminate the application of torque to the screw. However, such a mechanism increases the complexity and number of components of the mechanism.
It would be desirable to provide for automatic torque regulation in automated equipment without the need for forming the screwdriver in multiple parts.